What size carb do you have on your 440 ?

[WileERobby]

And just WHERE would I look this up?

The bottom line is that there is always a trade off when you are looking at street and race use. Most people want a balance of BOTH. In that case YOU have to decide how much you are going to give up in STREET manners. My point above is based on what the factory determined was on the edge of acceptable street manners for the maximum performance.

Yes, I agree with all this. But.. my only point was with your reasoning that cubes/weight has nothing to do with secondary choice. By that, you mean that, all else being equal, a 273 in a Dart or in an Imperial (using extremes as an example) would not factor in deciding what type of secondary to use ? Or, what if each car had a 440 in it ? You don't decide which, just on a camshaft; weight, transmission type, rear axle ratio... as well as intented use (street or track) all play a role.

 

[Cranky]

Even traction or lack there of can make a difference on the carb. I thought I had my 71 340 Cuda with TQ dialed in pretty good until I put slicks on it then it had a slight bog right off the line but it never did that with street tires. A slight secondary air door adjustment took care of that....

 

[696pack]

Yes, I agree with all this. But.. my only point was with your reasoning that cubes/weight has nothing to do with secondary choice. By that, you mean that, all else being equal, a 273 in a Dart or in an Imperial (using extremes as an example) would not factor in deciding what type of secondary to use ? Or, what if each car had a 440 in it ? You don't decide which, just on a camshaft; weight, transmission type, rear axle ratio... as well as intented use (street or track) all play a role.

You are mixing up even your own argument in this.

The simple answer to your question is that the weight of the car and weather it has mechanical vs. vacuum secondaries have absolutely NOTHING to do with the peformance of the car.

You did not answer my question as to where I should "look it up" for you to offer any facts to support your arguement.

You said:
"the weight of the car has very much to do with the decision of the type of secondary"

An engine is really nothing more than a big air pump. The more air you can put through it the more power it makes and the faster it will propel the car down the road.

Your example of the same size engine in different weight vehicles has nothing to do with the "need" for mechanical seconardies or them making the car perform any better.

A carb with vacuum secondaries "feed" the engine simply by the demand from the engine. Mechanicals "force" more fuel into the engine and often times the engine can't take that much fuel when feed that much and that is why the engine bogs. If you have a large enough cam and matching parts such as good flowing heads and headers then the engine "may" be able to take all of that fuel at one time.

 

[WileERobby]

You are mixing up even your own argument in this.

The simple answer to your question is that the weight of the car and weather it has mechanical vs. vacuum secondaries have absolutely NOTHING to do with the peformance of the car.

You did not answer my question as to where I should "look it up" for you to offer any facts to support your arguement.

You said:
"the weight of the car has very much to do with the decision of the type of secondary"

An engine is really nothing more than a big air pump. The more air you can put through it the more power it makes and the faster it will propel the car down the road.

Your example of the same size engine in different weight vehicles has nothing to do with the "need" for mechanical seconardies or them making the car perform any better.

A carb with vacuum secondaries "feed" the engine simply by the demand from the engine. Mechanicals "force" more fuel into the engine and often times the engine can't take that much fuel when feed that much and that is why the engine bogs. If you have a large enough cam and matching parts such as good flowing heads and headers then the engine "may" be able to take all of that fuel at one time.

Secondaries control air, not fuel. Fuel only enters thru idle,main,power, & accelerator circuits. Engines don't bog from too much fuel, they bog from too much air. Here's what I just pulled off Holley's info: QUESTION How do I know if a vacuum or mechanical carburetor is best for me?
ANSWER For street cars the vacuum secondary carburetor works best on midweight or heavyweight cars with an automatic transmission. They are more forgiving than a Double Pumper is because they work by sensing engine load. The mechanical secondary carburetor is best on a lighter car with radical camshaft and a lower gear and manual transmission or on a car that is going to be used for racing purposes.
I've always used DP's for the track. Vac's on street cars.

 

[696pack]

Secondaries control air, not fuel. Fuel only enters thru idle,main,power, & accelerator circuits. Engines don't bog from too much fuel, they bog from too much air. Here's what I just pulled off Holley's info: QUESTION How do I know if a vacuum or mechanical carburetor is best for me?
ANSWER For street cars the vacuum secondary carburetor works best on midweight or heavyweight cars with an automatic transmission. They are more forgiving than a Double Pumper is because they work by sensing engine load. The mechanical secondary carburetor is best on a lighter car with radical camshaft and a lower gear and manual transmission or on a car that is going to be used for racing purposes. I've always used DP's for the track. Vac's on street cars.

The last time I checked the fuel and air mixture remains the same throughout the power band so air or fuel it is all the same and they bog from that mixture.

You have just reinforced what I am saying. It has nothing to do with the weight of the car but rather the cam, gears, heads, headers, etc. as I said earlier.

 

[WileERobby]

The last time I checked the fuel and air mixture remains the same throughout the power band so air or fuel it is all the same and they bog from that mixture.

You have just reinforced what I am saying. It has nothing to do with the weight of the car but rather the cam, gears, heads, headers, etc. as I said earlier.

Actually, no. The fuel/air mixture does not remain the same. I guess you didn't read what the Holley carb people say about weight, either... I'm done here.

 

[696pack]

Actually, no. The fuel/air mixture does not remain the same. I guess you didn't read what the Holley carb people say about weight, either... I'm done here.

Oh really? I guess you will have to explain how that changes.

I read it and I don't care WHO said it, it isn't true. I have no idea why they would have thrown that in, likely just an employee that doesn't know any better.

 

[WileERobby]

Even traction or lack there of can make a difference on the carb. I thought I had my 71 340 Cuda with TQ dialed in pretty good until I put slicks on it then it had a slight bog right off the line but it never did that with street tires. A slight secondary air door adjustment took care of that....

Yes ! You are 100% correct, thank you. Why, because with the slicks, the carb is now subject to the full load (weight) of the vehicle. Whereas with the poorer traction with street tires, the full load is not transmitted because of tire spin.

 

[696pack]

Yes ! You are 100% correct, thank you. Why, because with the slicks, the carb is now subject to the full load (weight) of the vehicle. Whereas with the poorer traction with street tires, the full load is not transmitted because of tire spin.

This has NOTHING to do with the actual weight of the car. You will have the same situation with a light car as with a heavy car. It is simply a matter of how the car HOOKS and that puts additional load on the engine. If you prefer to equate this to a heavier car then go ahead and entertain yourself with that thought.

 

[WileERobby]

This has NOTHING to do with the actual weight of the car. You will have the same situation with a light car as with a heavy car. It is simply a matter of how the car HOOKS and that puts additional load on the engine. If you prefer to equate this to a heavier car then go ahead and entertain yourself with that thought.

And the definition of "load" is ? a : a mass or weight supported by something <branches bent low by their load of fruit> b : the forces to which a structure is subjected due to superposed weight or to wind pressure on the vertical surfaces; broadly : the forces to which a given object is subjected

 

[696pack]

And the definition of "load" is ? a : a mass or weight supported by something <branches bent low by their load of fruit> b : the forces to which a structure is subjected due to superposed weight or to wind pressure on the vertical surfaces; broadly : the forces to which a given object is subjected

Even though you didn't, I think what you are trying to convey is that when the tires hook the load seem heavier. It isn't but it DOES then take more force (h.p.) to move it. Think of it as though the wheels are stuck in mud. The car isn't any heavier but it does take more force (power) to move it.

Lets get back to our original arguement. I also think what you are trying to imply from above somehow to support your arguement is that you need mechanical secondaries for a bigger/heavier load. What you REALLY need is more POWER. Mechanical secondaries by themself will not give you more power.

Here is another way for you to look at this that you might be better able to understand. Same factory stock engine each with a factory speced carb with the same cfm rating. One with vacuum secondaries one with mechanicals. Mash the pedal to the floor on both and see which one pulls away from the other. The vacuum carb every time. Why? The engine can't take all the fuel you are attempting to give it all at one time. The vacuum carb is only feeding the engine the amount of fuel it can use at any given time due to the vacuum the engine is creating.

The only time a same size mechanical carb is superior to a vacuum carb is if the engine is built (bigger cam etc.) to the point it can take all of the gas the mechanical carb is attempting to deliver to it.

I don't know how to better explain this, maybe someone else can because I am done with it.

 

[WileERobby]

Even though you didn't, I think what you are trying to convey is that when the tires hook the load seem heavier. It isn't but it DOES then take more force (h.p.) to move it. Think of it as though the wheels are stuck in mud. The car isn't any heavier but it does take more force (power) to move it.

Lets get back to our original arguement. I also think what you are trying to imply from above somehow to support your arguement is that you need mechanical secondaries for a bigger/heavier load. What you REALLY need is more POWER. Mechanical secondaries by themself will not give you more power.

Here is another way for you to look at this that you might be better able to understand. Same factory stock engine each with a factory speced carb with the same cfm rating. One with vacuum secondaries one with mechanicals. Mash the pedal to the floor on both and see which one pulls away from the other. The vacuum carb every time. Why? The engine can't take all the fuel you are attempting to give it all at one time. The vacuum carb is only feeding the engine the amount of fuel it can use at any given time due to the vacuum the engine is creating.

The only time a same size mechanical carb is superior to a vacuum carb is if the engine is built (bigger cam etc.) to the point it can take all of the gas the mechanical carb is attempting to deliver to it.

I don't know how to better explain this, maybe someone else can because I am done with it.

When the tires hook, the load IS greater. If you don't understand physics, I don't know what to say. Traction is needed to get out of mud (don't the tires spin in mud ? ) You're all over the place with your analogy, you don't add an external variable to the equation. And again, secondaries (and primaries for that matter) control AIR, not fuel. If you don't understand how a carburetor works, I don't know what to say. I could get into technicalities, involving piston speed, rpm, air velocity, fuel mass, load force, inertia, etc. I understand quite well the physics of carburetor operation, but I'd rather not divulge my qualifications on this matter.

 

[696pack]

When the tires hook, the load IS greater. If you don't understand physics, I don't know what to say. Traction is needed to get out of mud (don't the tires spin in mud ? ) You're all over the place with your analogy, you don't add an external variable to the equation. And again, secondaries (and primaries for that matter) control AIR, not fuel. If you don't understand how a carburetor works, I don't know what to say. I could get into technicalities, involving piston speed, rpm, air velocity, fuel mass, load force, inertia, etc. I understand quite well the physics of carburetor operation, but I'd rather not divulge my qualifications on this matter.

Didn't wnat to discuss any further but it is about the force required pull a car out of the mud which is POWER.

Again, ther is a direct relationship between air and fuel It is all the same thing. The more you can put throught the engine the more power, but the engine hase to be able to take it as it is being feed sand if it can't take it all at one time it is going to bog.

Please, enlighten me with your knowledge and qualifications. I have only been around these cars since I was driving them new so I don't really know a lot about them.

 

[Meep-Meep]

Vacuum vs. mechanical secondaries and CFM play a big role in determining which carb is right for the application (bigger than most people think) but the individual also must consider the other circuits and how they affect the fuel metering from idle to WOT. Double pumpers are really race only carbs because the balance of the main jetting and PVCR restriction is favored toward the WOT throttle position while the OEM and "street" carbs favor part throttle drivability because most of the time the engine is relying on the transfer slot to meter fuel. In the case of the original poster I would lean (pun intended) toward the vac secondary or AFB but a model with an emphasis on street rather than race. Ask yourself how much time do you spend at WOT vs. part throttle?

Fuel delivery is completely dependent on air velocity through the venturies. The low pressure at the main discharge nozzle creates a pressure difference and the higher atmosphere pressure in the bowl pushes the fuel out. Picking the correct venturi size for the application is mandatory otherwise the rest of the circuits won't work properly.

The emulsion tubes and high speed bleeds are calibrated to deliver the proper A/F ratio based on air flow through the venturi and if that's not as designed then everything else is wrong. It is possible to adjust the A/F ratio at different RPM and load requirements by only adjusting the holes in the emulsion tubes and the size of the high speed bleed. When you think about it the main jet is kind of a crude adjustment and the range of sizes for a given carb should be limited. At some point if the carb doesn't work properly you have to admit that you have the wrong carb.

Dick Landy did very well in the super stock class with an 11 sec 69 R/T 440 Charger and he was running the factory AVS jetted one percent richer in the primaries with a CH4B dual plane intake. I ran a factory 440 AVS on my 68 383 RR and it ran mid 12's and I had stock jetting. How bad can a factory late 60's carb be? After all they were designed to support 375-400 HP on a 400+ CI engine. Yes, they were somewhat on the lean side for the CAP but still very useable in my opinion.

 

[rustycopcar]

i have an eddy 750cfm factory set for preformance on my 318. (over carb'd much?) i got it to replace that pos carter 250cfm 2bbl carb. i put on an eddy preformer rpm intake on it ant its got tons more power. this is the same carb i will be using for the 440 im building. i changed my mind to go big or go home so ill keep you updated on how it goes. to add to that if you dont have the ignition to back it up you wont do nearly as well. i have MSD in mine now and it brought be back uo in hp and efficency if you consider 11 mpg awesome.